perf(rust): Drop probe tables in parallel in new-streaming equi-join

[orlp]

This was a partial single-threaded bottleneck.

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.09%. Comparing base (db1684d) to head (d65c712).
Report is 25 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-stream/src/nodes/joins/equi_join.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20373      +/-   ##
==========================================
- Coverage   79.10%   79.09%   -0.01%     
==========================================
  Files        1572     1572              
  Lines      219958   219962       +4     
  Branches     2465     2465              
==========================================
- Hits       173991   173986       -5     
- Misses      45399    45408       +9     
  Partials      568      568              

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